Endoscope system, processor device of endoscope system, and image processing method

ABSTRACT

Broadband light BB and narrowband light NB are simultaneously irradiated to a subject. A blue signal B, a green signal G, and a red signal R are obtained by imaging the subject using a color CCD  33 . A base image is generated from the signals B, G, and R of three colors. A B/G image having a B/G ratio is generated. A superficial blood vessel extraction image is obtained by extracting a pixel, in which the B/G ratio is equal to or less than a boundary value Ls between the mucous membrane and the superficial blood vessel, from the B/G image. A medium-deep blood vessel extraction image is obtained by extracting a pixel, in which the B/G ratio is equal to or greater than a boundary value Ld between the mucous membrane and the medium-deep blood vessel. The boundary values Ls and Ld differ depending on each observation mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2013/050359 filed on Jan. 11, 2013, which claims priority under 35U.S.C §119(a) to Japanese Patent Application No. 2012-013316 filed Jan.25, 2012. Each of the above applications is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an endoscope system capable ofextracting blood vessels, such as superficial blood vessels andmedium-deep blood vessels, in a subject, a processor device of anendoscope system, and an image processing method.

2. Description of the Related Art

In recent medical treatment, diagnosis or the like using an endoscopeapparatus has been widely performed. As observation of the inside of asubject using an endoscope apparatus, not only normal observation usingwhite light of broadband light as illumination light but also bloodvessel enhancement observation, in which blood vessels in a subject arehighlighted using narrowband light having a narrowband wavelength, hasbeen performed.

In this blood vessel enhancement observation, determination regardingwhether or not cancer is present from the shape of a blood vessel isperformed. Types of blood vessels mainly include superficial bloodvessels distributed on a living tissue surface and medium-deep bloodvessels located below the superficial blood vessels. Depending on thepurpose of diagnosis, diagnosis may be performed focusing on certainblood vessels. In this case, if blood vessels that are not the focus ofobservation are added in an endoscope image, there may be aninterruption to diagnosis. For this reason, differentiating superficialblood vessels or medium-deep blood vessels from the image and displayingan image, which is obtained by extracting only blood vessels to beobserved, on a monitor has been demanded.

Regarding the method of determining the depth of a blood vessel,JP2011-135983A discloses a method of performing determination of asuperficial blood vessel when the hue of a narrowband image generatedbased on narrowband light in a specified wavelength region (415 nm, 540nm) is 5 to 35 and performing determination as a medium-deep bloodvessel when the hue is 170 to 200.

SUMMARY OF THE INVENTION

In observation of the body cavity using an endoscope, depending on apart, for example, in the esophagus and the stomach, the amount ofreturn light from the subject may be different even if the esophagus andthe stomach are illuminated with light having the same light amount.That is, the appearance or color of the blood vessel may changedepending on the part If the color of the blood vessel changes in thisway, it is difficult to reliably distinguish superficial blood vesselsand medium-deep blood vessels with a blood vessel discrimination methodbased on the hue disclosed in JP2011-135983A.

The present invention has been made in view of the above-background, andit is an object of the present invention to provide an endoscope systemcapable of reliably extracting a plurality of types of blood vessels atdifferent depths even if a part to be observed is changed, a processordevice of an endoscope system, and an image processing method.

In order to achieve the above-described object, an endoscope system ofthe present invention includes: an illumination unit for irradiating asubject with illumination light including a blue component and a greencomponent; an image signal acquisition unit for acquiring two or morecolor signals having different pieces of color information by receivingand imaging return light from the subject using an imaging element; amulti-color image generation unit for generating a multi-color imageformed from calculated values obtained by performing predeterminedcalculation for each pixel using the two or more color signals; and ablood vessel extraction image generation unit for generating at leastone of a first layer blood vessel extraction image, which is obtained byextracting a first layer blood vessel at a specific depth from themulti-color image, and a second layer blood vessel extraction image,which is obtained by extracting a second layer blood vessel at aposition deeper than the first layer blood vessel from the multi-colorimage, by performing blood vessel extraction processing, which differsdepending on each of a plurality of observation modes, on themulti-color image.

Preferably, the blood vessel extraction image generation unit includes aplurality of calculated value tables, which are provided for each of theplurality of observation modes and store a correlation between a mucousmembrane, the first layer blood vessel, and the second layer bloodvessel of the subject and the calculated values, and a blood vesselextraction image generation section that generates at least one of thefirst layer blood vessel extraction image and the second layer bloodvessel extraction image by performing blood vessel extraction processingusing a calculated value table corresponding to the set observationmode.

Preferably, in each of the calculated value tables, a calculated valueindicating a boundary between the mucous membrane and the first layerblood vessel is stored as a first boundary value, and a calculated valueindicating a boundary between the mucous membrane and the second layerblood vessel is stored as a second boundary value. Preferably, the firstand second boundary values differ depending on each calculated valuetable. Preferably, the plurality of observation modes are modes forimproving visibility of a blood vessel in a predetermined part of thesubject, and each of the observation modes is set for each predeterminedpart.

It is preferable to further include a blood vessel enhancement image orsuppression image generation unit for generating a first layer bloodvessel enhancement image or suppression image, in which the first layerblood vessel is enhanced or suppressed, using the first layer bloodvessel extraction image or generating a second layer blood vesselenhancement image or suppression image, in which the second layer bloodvessel is enhanced or suppressed, using the second layer blood vesselextraction image. It is preferable to further include a display unit fordisplaying at least one of the first layer blood vessel enhancementimage or suppression image and the second layer blood vessel enhancementimage or suppression image.

Preferably, the illumination unit simultaneously irradiates bluenarrowband light and fluorescent light that is wavelength-converted by awavelength conversion member using the blue narrowband light, as theillumination light, toward the subject, and the image signal acquisitionunit images the subject, to which the blue narrowband light and thefluorescent light are irradiated simultaneously, using a color imagingelement. As another implementation means, it is preferable that theillumination unit sequentially irradiate blue narrowband light and greennarrowband light, as the illumination light, toward the subject and theimage signal acquisition unit image the subject sequentially using amonochrome imaging element whenever the blue narrowband light and thegreen narrowband light are sequentially irradiated. Preferably, thecolor signals include a blue signal having information of a bluecomponent and a green signal having information of a green component,and the multi-color image is a B/G image having a B/G ratio obtained bydividing the blue signal by the green signal for each pixel.

Other aspect of the present invention is a processor device of anendoscope system including an electronic endoscope that irradiates asubject with illumination light including a blue component and a greencomponent and acquires two or more color signals having different piecesof color information by receiving and imaging return light from thesubject using an imaging element. The processor device of an endoscopesystem includes: a multi-color image generation unit for generating amulti-color image formed from calculated values obtained by performingpredetermined calculation for each pixel using the two or more colorsignals and a blood vessel extraction image generation unit forgenerating at least one of a first layer blood vessel extraction image,which is obtained by extracting a first layer blood vessel at a specificdepth from the multi-color image, and a second layer blood vesselextraction image, which is obtained by extracting a second layer bloodvessel at a position deeper than the first layer blood vessel from themulti-color image, by performing blood vessel extraction processing,which differs depending on each of a plurality of observation modes, onthe multi-color image.

Other aspect of the present invention is an image processing methodperformed in an endoscope system including an electronic endoscope thatirradiates a subject with illumination light including a blue componentand a green component and acquires two or more color signals havingdifferent pieces of color information by receiving and imaging returnlight from the subject using an imaging element. The image processingmethod includes: generating a multi-color image formed from calculatedvalues obtained by performing predetermined calculation for each pixelusing the two or more color signals; and generating at least one of afirst layer blood vessel extraction image, which is obtained byextracting a first layer blood vessel at a specific depth from themulti-color image, and a second layer blood vessel extraction image,which is obtained by extracting a second layer blood vessel at aposition deeper than the first layer blood vessel from the multi-colorimage, by performing blood vessel extraction processing, which differsdepending on each of a plurality of observation modes, on themulti-color image.

According to the present invention, different blood vessel extractionprocessing is performed for each of a plurality of observation modes.Therefore, even if a part to be observed is changed, a plurality oftypes of blood vessels at different depths can be reliably extracted byperforming switching to the observation mode corresponding to the part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view of an endoscope system.

FIG. 2 is a block diagram showing the electrical configuration of anendoscope system of a first embodiment.

FIG. 3 is a graph showing the emission spectra of broadband light andnarrowband light.

FIG. 4 is a graph showing the emission spectra of blue laser light andemitted excitation light that is excited and emitted by applying theblue laser light to a phosphor.

FIG. 5 is a graph showing the spectral transmittances of color filtersof R, G, and B colors.

FIG. 6 is a graph showing the relationship between the blood vesseldepth and the B/G ratio that is stored in a first observation modetable.

FIG. 7 is a diagram for explaining the B/G ratio of the mucous membrane,the superficial blood vessel, and the medium-deep blood vessel whenreturn light, in which the ratio between the B and G components isapproximately the same, is received.

FIG. 8 is a graph showing the relationship between the blood vesseldepth and the B/G ratio that is stored in a second observation modetable

FIG. 9 is a diagram for explaining the B/G ratio of the mucous membrane,the superficial blood vessel, and the medium-deep blood vessel whenreturn light, in which the percentage of the B component is larger thanthe percentage of the G component, is received.

FIG. 10 is a graph showing the relationship between the blood vesseldepth and the B/G ratio that is stored in a third observation modetable.

FIG. 11 is a diagram for explaining the B/G ratio of the mucousmembrane, the superficial blood vessel, and the medium-deep blood vesselwhen return light, in which the percentage of the G component is largerthan the percentage of the B component, is received.

FIG. 12 is an image diagram showing an image in which the superficialblood vessel is enhanced and the medium-deep blood vessel is suppressed.

FIG. 13 is an image diagram showing an image in which the superficialblood vessel is suppressed and the medium-deep blood vessel is enhanced.

FIG. 14 is a flowchart showing the operation of one embodiment of thepresent invention.

FIG. 15 is a block diagram showing the electrical configuration of anendoscope system of a second embodiment.

FIG. 16 is a schematic diagram of a rotary filter.

FIG. 17A is a graph showing the relationship between the blood vesseldepth and the B−G difference that is stored in a first observation modetable.

FIG. 17B is a graph showing the relationship between the blood vesseldepth and the B−G difference that is stored in a second observation modetable.

FIG. 17C is a graph showing the relationship between the blood vesseldepth and the B−G difference that is stored in a third observation modetable.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, an electronic endoscope system 10 of a firstembodiment includes an electronic endoscope 11 that images the inside ofa subject, a processor device 12 that generates an endoscope image basedon a signal obtained by imaging, a light source device 13 (a form of anillumination unit) that generates light for illuminating the subject,and a monitor 14 that displays an endoscope image. The electronicendoscope 11 includes a flexible insertion unit 16 that is inserted intothe body cavity, an operating unit 17 provided at the proximal end ofthe insertion unit 16, and a universal code 18 that makes a connectionbetween the operating unit 17 and the processor device 12 and the lightsource device 13.

The electronic endoscope system 10 has a function of generating asuperficial blood vessel enhancement image or suppression image, inwhich a superficial blood vessel of a subject is enhanced/suppressed,and a medium-deep blood vessel enhancement image or suppression image,in which a medium-deep superficial blood vessel is enhanced/suppressed.Which blood vessel enhancement image or suppression image is to begenerated is determined by the operation of a superficial layer andmedium-deep layer selection SW 28 (refer to FIG. 2). In endoscopicobservation, the appearance of the blood vessel changes with each part,such as the stomach, colon, and esophagus. Accordingly, there is afunction of correcting this. The appearance of the blood vessel changeswith the ratio P between a blue component (B component) and a greencomponent (G component) of return light (reflected light or the like)that is returned from the subject. Here, it is assumed that theobservation mode of a part for which the percentage of the B componentis approximately the same as the percentage of the G component is afirst observation mode, the observation mode of a part for which thepercentage of the B component is larger than the percentage of the Gcomponent is a second observation mode, and the observation mode of apart for which the percentage of the G component is larger than thepercentage of the B component is a third observation mode. The first tothird observation modes can be switched when an operator operates anobservation mode selection SW 29 according to a part to be observed(refer to FIG. 2).

A curved portion 19 obtained by connecting a plurality of curved piecesis formed at the distal end of the insertion unit 16. The curved portion19 is curved in the horizontal and vertical directions by operating anangle knob 21 of the operating unit. A distal portion 16 a including anoptical system for imaging the body cavity and the like is provided atthe distal end of the curved portion 19. The distal portion 16 a isdirected in a desired direction within the body cavity by the bendingoperation of the curved portion 19.

A connector 24 is attached to the universal code 18 on the side of theprocessor device 12 and the light source device 13. The connector 24 isa composite connector including a communication connector and a lightsource connector, and the electronic endoscope 11 is detachablyconnected to the processor device 12 and the light source device 13through the connector 24.

As shown in FIG. 2, the light source device 13 includes a broadbandlight source 30, a narrowband light source 33, and a coupler 36. Asshown in FIG. 3, the broadband light source 30 generates broadband lightBB in a wavelength range from the blue region to the red region (about400 nm to 700 nm). The broadband light source 30 is always ON while theelectronic endoscope 11 is used. The broadband light BB emitted from thebroadband light source 30 is incident on a broadband optical fiber 40.As the broadband BB, not only white light of a xenon lamp or the likebut also white light (refer to FIG. 4 for the emission spectrum), whichis obtained by combining laser light having a center wavelength of 445nm with emitted excitation light of 460 nm to 700 nm that is excited andemitted from a phosphor by the laser light, may be used.

The narrowband light source 33 is a light emitting diode (LED), a laserdiode (LD), or the like. As shown in FIG. 3, the narrowband light source33 generates narrowband light NB having a limited wavelength of 400±10nm (center wavelength of 405 nm). The narrowband light NB emitted fromthe narrowband light source 33 is incident on a narrowband optical fiber33 a. In addition, the wavelength of the narrowband light NB is notlimited to 400±10 nm (center wavelength of 405 nm). For example,narrowband light having a wavelength of 440±10 nm (center wavelength of445 nm) may be used.

The coupler 36 connects a light guide 43 in the electronic endoscope 11to the broadband optical fiber 40 and the narrowband optical fiber 33 a.Therefore, both the broadband light BB and the narrowband light NB aresimultaneously incident on the light guide 43.

The electronic endoscope 11 includes the light guide 43, a CCD 44, ananalog processing circuit 45 (analog front end: AFE), and an imagingcontrol unit 46. The light guide 43 is a large-diameter optical fiber, abundle fiber, or the like, and the incidence end is inserted into thecoupler 36 in the light source device and the exit end is directedtoward an irradiation lens 48 provided in the distal portion 16 a. Thebroadband light BB and the narrowband light NB guided by the light guide43 are irradiated into the subject through the irradiation lens 48 andan illumination window 49 attached to the end surface of the distalportion 16 a. The broadband light BB and the narrowband light NBreflected within the subject are incident on a condensing lens 51through an observation window 50 attached to the end surface of thedistal portion 16 a.

The CCD 44 receives light from the condensing lens 51 through an imagingsurface 44 a, performs photoelectric conversion of the received lightand accumulates signal charges, and reads the accumulated signal chargesas an imaging signal. The read imaging signal is transmitted to an AFE45. The CCD 44 is a color CCD, and pixels of three colors of a B pixelin which a color filter of B color is provided, a G pixel in which acolor filter of G color is provided, and an R pixel in which a colorfilter of R color is provided are arrayed on the imaging surface 44 a. Aform of an image signal acquisition unit is configured to include thecondensing lens 51, the CCD 44 having the imaging surface 44 a, and theAFE 45.

The color filters of B, G, and R colors have transmission distributions52, 53, and 54, respectively, as shown in FIG. 5. When only thebroadband light BB having a wavelength region of about 400 nm to 700 nmis incident on the CCD 44, the color filters of B, G, and R colors allowlight having a wavelength corresponding to the transmissiondistributions 52, 53, and 54, of the broadband light BB, to betransmitted therethrough. Here, it is assumed that a signalphotoelectrically converted by the R pixel is a red signal R, a signalphotoelectrically converted by the G pixel is a green signal G, and asignal photoelectrically converted by the B pixel is a blue signal B.

The AFE 45 is configured to include a correlated double sampling circuit(CDS), an automatic gain control circuit (AGC), and an analog/digitalconverter (A/D) (all not shown). The CDS performs correlated doublesampling processing on an imaging signal from the CCD 44 to remove noisecaused by the driving of the CCD 44. The AGC amplifies an imaging signalfrom which noise has been removed by the CDS. The A/D converts animaging signal amplified by the AGC into a digital imaging signal of apredetermined number of bits, and inputs the digital imaging signal tothe processor device 12.

The imaging control unit 46 is connected to a controller 59 in theprocessor device 12, and transmits a driving signal to the CCD 44 whenthere is an instruction from the controller 59. The CCD 44 outputs animaging signal to the AFE 45 at a predetermined frame rate based on thedriving signal from the imaging control unit 46.

As shown in FIG. 2, the processor device 12 includes a base imagegeneration unit 55, a frame memory 56, an image processing unit 57, anda display control circuit 58. The controller 59 controls each of theunits. The base image generation unit 55 generates a base image byperforming various kinds of signal processing on the blue signal B, thegreen signal G, and the red signal R output from the AFE 45 of theelectronic endoscope. The generated base image is temporarily stored inthe frame memory 56. The blue signal B, the green signal G, and the redsignal R output from the AFE 45 are stored in the frame memory 56. Thebase image may be a normal observation image, which is obtained by usingonly the broadband light BB without using the narrowband light NB, or apseudo color image, which is obtained by pseudo coloring of blood vesselfunction information, such as oxygen saturation.

The image processing unit 57 includes a B/G image generation section 61(a form of a multi-color image generation unit), a blood vesselextraction image generation section 63, and a blood vessel enhancementimage or suppression image generation section 65 (a form of a bloodvessel enhancement image or suppression image generation unit). The B/Gimage generation section 61 generates a B/G image having a brightnessratio B/G (B/G ratio) between the blue signal B and the green signal G.Here, the B/G ratio indicates a brightness ratio of pixels at the sameposition between the blue signal B and the green signal G.

The blood vessel extraction image generation section 63 generates asuperficial blood vessel extraction image by extracting the superficialblood vessel based on the B/G image, or generates a medium-deep bloodvessel extraction image by extracting the medium-deep blood vessel basedon the B/G image. The method of generating the blood vessel extractionimages differs depending on which of the first to third observationmodes is set. When the first observation mode is set, a superficialblood vessel extraction image or a medium-deep blood vessel extractionimage is generated using a first observation mode table 63 a.Correlation between the brightness ratio B/G and the blood vessel depthshown in FIG. 6 is stored in the first observation mode table 63 a. Thiscorrelation is a proportional relationship in which the brightness ratioB/G (B/G ratio) increases as the blood vessel depth increases. Inaddition, a form of a blood vessel extraction image generation unit isconfigured to include a blood vessel extraction image generation section63 and the first observation mode table 63 a to a third observation modetable 63 c.

In the first observation mode, the percentage of the blue wavelengthcomponent (B component) of return light from the subject isapproximately the same as the percentage of the green wavelengthcomponent (G component) of the return light. Therefore, as shown in FIG.7, when the illumination light is irradiated to the mucous membrane withno blood vessels, the ratio of the B and G components of the returnlight is approximately fixed. This is because there is no large lightabsorption in the mucous membrane. Assuming that the average B/G ratioin this case is P, the B/G ratio in the mucous membrane falls within afixed range of “Ls to P to Ld”. Here Ls is a lower limit of the B/Gratio of the mucous membrane in the first observation mode, and Ld is anupper limit of the B/G ratio of the mucous membrane in the firstobservation mode.

When illumination light is irradiated to a superficial blood vessel, theB component of the illumination light is largely absorbed by thesuperficial blood vessel, while the G component is not absorbed almost.For this reason, the B/G ratio is equal to or less than Ls in mostcases. Therefore, it can be seen that the superficial blood vessel isprojected to the pixel having a B/G ratio equal to or less than Ls (thatis, Ls is a boundary value between the mucous membrane and thesuperficial blood vessel). On the other hand, when illumination light isirradiated to a medium-deep blood vessel, the G component of theillumination light is largely absorbed by the medium-deep blood vessel,while the B component is not absorbed almost. For this reason, the B/Gratio is equal to or greater than Ld in most cases. Therefore, it can beseen that the medium-deep blood vessel is projected to the pixel havinga B/G ratio equal to or larger than Ld (that is, Ld is a boundary valuebetween the mucous membrane and the medium-deep blood vessel).

Accordingly, when generating a superficial blood vessel extraction imagein the first observation mode, only the pixel value of a pixel having aB/G ratio equal to or less than Ls is extracted from the B/G image, andbinarization processing for setting the pixel values of other pixels to0 is performed. On the other hand, when generating a medium-deep bloodvessel extraction image, only the pixel value of a pixel having a B/Gratio equal to or greater than Ld is extracted from the B/G image, andbinarization processing for setting the pixel values of other pixels to0 is performed.

When the second observation mode is set, a superficial blood vesselextraction image or a medium-deep blood vessel extraction image isgenerated using the second observation mode table 63 b. As shown in FIG.8, similar to the first observation mode table 63 a, the secondobservation mode table 63 b shows a proportional relationship in whichthe brightness ratio B/G (B/G ratio) increases as the blood vessel depthincreases. In the second observation mode, as shown in FIG. 9, since thepercentage of the blue wavelength component (B component) of returnlight from the subject is larger than the percentage of the greenwavelength component (G component) of the return light, the B/G ratio isgenerally high. Accordingly, a boundary value Ls′ between the mucousmembrane and the superficial blood vessel is larger than the boundaryvalue Ls in the first observation mode, and a boundary value Ld′ betweenthe mucous membrane and the medium-deep blood vessel is larger than theboundary value Ld in the first observation mode.

Therefore, when generating a superficial blood vessel extraction imagein the second observation mode, only the pixel value of a pixel having aB/G ratio equal to or less than Ls′ is extracted from the B/G image, andbinarization processing for setting the pixel values of other pixels to0 is performed. On the other hand, when generating a medium-deep bloodvessel extraction image, only the pixel value of a pixel having a B/Gratio equal to or greater than Ld′ is extracted from the B/G image, andbinarization processing for setting the pixel values of other pixels to0 is performed.

When the third observation mode is set, a superficial blood vesselextraction image or a medium-deep blood vessel extraction image isgenerated using the third observation mode table 63 c. As shown in FIG.10, similar to the first observation mode table 63 a, the thirdobservation mode table 63 c shows a proportional relationship in whichthe brightness ratio B/G (B/G ratio) increases as the blood vessel depthincreases. In the third observation mode, as shown in FIG. 11, since thepercentage of the green wavelength component (G component) of returnlight from the subject is larger than the percentage of the bluewavelength component (B component) of the return light, the B/G ratio isgenerally low. Accordingly, a boundary value Ls″ between the mucousmembrane and the superficial blood vessel is smaller than the boundaryvalue Ls in the first observation mode, and a boundary value Ld″ betweenthe mucous membrane and the medium-deep blood vessel is smaller than theboundary value Ld in the first observation mode.

Therefore, when generating a superficial blood vessel extraction imagein the third observation mode, only the pixel value of a pixel having aB/G ratio equal to or less than Ls″ is extracted from the B/G image, andbinarization processing for setting the pixel values of other pixels to0 is performed. On the other hand, when generating a medium-deep bloodvessel extraction image, only the pixel value of a pixel having a B/Gratio equal to or greater than Ld″ is extracted from the B/G image, andbinarization processing for setting the pixel values of other pixels to0 is performed.

From diagnosis and the like until now, it has been found that therelationship of the average B/G ratio in each part of the esophagus,colon, and stomach is B/G ratio of esophagus>B/G ratio of colon>B/Gratio of stomach. Therefore, it is preferable to set the firstobservation mode when observing the colon, set the second observationmode when observing the esophagus, and set the third observation modewhen observing the stomach, although this also depends on the purpose ofdiagnosis and other observation conditions.

The blood vessel enhancement image or suppression image generationsection 65 generates a superficial blood vessel enhancement image orsuppression image, in which a superficial blood vessel is enhanced (orsuppressed), by combining the superficial blood vessel extraction imageand the base image, and generates a medium-deep blood vessel enhancementimage or suppression image, in which a medium-deep blood vessel isenhanced (or suppressed), by combining the medium-deep blood vesselextraction image and the base image. When enhancing the blood vessel avalue obtained by increasing the pixel value of each pixel in thesuperficial blood vessel extraction image (or a medium-deep blood vesselextraction image several times is added to the pixel value of each pixelof the base image. When suppressing the blood vessel, a value obtainedby increasing the pixel value of each pixel in the superficial bloodvessel extraction image (or a medium-deep blood vessel extraction image)several times is subtracted from the pixel value of each pixel of thebase image.

The display control circuit 58 displays the blood vessel enhancementimage or suppression image on the monitor 14 (a form of a display unit).For example, as shown in FIG. 12, when a superficial blood vessel 71extracted from the B/G image is enhanced on the blood vessel enhancementimage or suppression image, diagnosis focusing on only the superficialblood vessel 71 is possible since the superficial blood vessel 71 isnoticeable compared with a medium-deep blood vessel 72, In contrast, asshown in FIG. 13, when the medium-deep blood vessel 72 extracted fromthe B/G image is enhanced on the blood vessel enhancement image orsuppression image, diagnosis focusing on only the medium-deep bloodvessel 72 is possible since the medium-deep blood vessel 72 isnoticeable compared with the superficial blood vessel 71.

As described above, by extracting only an image of the blood vessel tobe observed from the B/G image and generating a blood vessel enhancementimage or suppression image using the extracted blood vessel image, onlythe blood vessel portion to be observed can be reliablyenhanced/suppressed without eliminating the information of portionsother than the blood vessel, for example, the information of unevennessof a part to be observed. Therefore, since not only the blood vesselinformation but also a lot of information useful for diagnosis, such asunevenness of a part to be observed, can be provided to the user, it ispossible to improve the diagnostic performance. In addition, since bloodvessels are divided into the superficial blood vessel and themedium-deep blood vessel so as to be separately extracted and each ofthe superficial blood vessel and the medium-deep blood vessel isseparately enhanced/suppressed, diagnosis focusing on the superficialblood vessel or diagnosis focusing on the medium-deep blood vessel ispossible.

Next, the operation of one embodiment of the present invention will bedescribed with reference to the flowchart shown in FIG. 14. First, anobservation mode corresponding to a part among the first to thirdobservation modes is set. The broadband light BB and the narrowbandlight NB emitted from the light source device 13 are irradiatedsimultaneously into the subject through the light guide 43. Reflectedlight from the subject is imaged by the color CCD 44. A base image isgenerated from the blue signal B, the green signal G, and the red signalR obtained by this imaging. The generated base image, the blue signal B,the green signal G, and the red signal R are temporarily stored in theframe memory 56.

Then, the B/G image generation section 61 generates a B/G image havingthe brightness ratio B/G between the blue signal B and the green signalG. A superficial blood vessel extraction image is generated byextracting the superficial blood vessel from the B/G image, and amedium-deep blood vessel extraction image is generated by extracting themedium-deep blood vessel from the B/G image. An observation mode tablecorresponding to the set observation mode is used for the blood vesselextraction. If the blood vessel extraction image is generated, a bloodvessel enhancement image or suppression image in which a superficialblood vessel (or a medium-deep blood vessel) is enhanced/suppressed isgenerated from the superficial blood vessel extraction image (or themedium-deep blood vessel extraction image) and the base image. Thegenerated blood vessel enhancement image or suppression image isconverted into a signal, which can be displayed on a monitor, by thedisplay control circuit 58 and is then image-displayed on the monitor 14as shown in FIG. 12 or 13.

In the first embodiment described above, the broadband light BB isemitted from the broadband light source 30 in the light source device13. However, instead of this, fluorescent light may be emitted byproviding a phosphor in the distal portion 16 a of the electronicendoscope 11 and exciting the phosphor with excitation light from anexcitation light source provided in the light source device 13. In thiscase, light obtained by combining fluorescent light and excitationlight, which is not absorbed by the phosphor, is irradiated into thesubject as the broadband light BB.

In the second embodiment of the present invention, unlike in the firstembodiment in which two types of illumination light beams to illuminatea subject are simultaneously irradiated, two types of illumination lightbeams are separately irradiated in a sequential manner. Here, as twotypes of illumination light beams, blue narrowband light GN having acenter wavelength of 415 nm and green narrowband light BN having acenter wavelength of 540 nm are sequentially irradiated. Accordingly, inan electronic endoscope system 100 of the second embodiment, as shown inFIG. 15, a rotary filter 101 and a motor 102 for rotating the rotaryfilter 101 at the fixed speed are used to irradiate the blue narrowbandlight BN and the green narrowband light GN sequentially. In addition, inorder to image the inside of the subject, a monochrome CCD 101 in whichno color filter is provided is used instead of the color CCD 44.

As shown in FIG. 16, in the rotary filter 101, a blue filter 101 a,through which the blue narrowband light BN (having a wavelength regionof 380 nm to 430 nm) having a center wavelength of 415 nm of thebroadband light BB from the broadband light source 30 is transmitted,and a green filter 101 b, through which the green narrowband light GN(having a wavelength region of 520 nm to 560 nm) having a centerwavelength of 540 nm of the broadband light is transmitted, are providedin the circumferential direction. Therefore, the blue narrowband lightBN and the green narrowband light GN are separately irradiated in asequential manner toward the light guide 43 due to the rotation of therotary filter 101.

The base image generation method and the B/G image generation methodbased on the sequential irradiation of the blue narrowband light BN andthe green narrowband light GN described above are different from thosein the first embodiment of the simultaneous irradiation method. Othersin the second embodiment are the same as in the first embodiment. Whengenerating a base image, a blue narrowband signal obtained whenirradiating and capturing the blue narrowband light BN is assigned tothe B and G channels for monitor display, and a green narrowband signalobtained when irradiating and capturing the green narrowband light GN isassigned to the R channel for monitor display, thereby generating thebase image. When generating a B/G image, the B/G image is generated fromthe brightness ratio between the blue narrowband signal and the greennarrowband signal.

In the embodiment described above, medium-deep blood vessels andsuperficial blood vessels are separated from each other using the B/Gratio. Instead of this, the blood vessels can also be separated usingcalculation values obtained by calculation using two or more colorsignals having different pieces of color information, such as a G/Bratio, a B−G difference, a G−B difference, a B/(B+G) ratio, a G/(B+G)ratio, a B/R ratio, an RIB ratio, a B−R difference, an R−B difference,and a RN ratio.

As in the embodiment described above, the relationship between thecalculated value and the blood vessel depth is stored in a plurality oftables corresponding to the first to third observation modes, and theboundary value of the calculated value indicating the boundary betweenthe mucous membrane and the superficial blood vessel and the boundaryvalue of the calculated value indicating the boundary between the mucousmembrane and the medium-deep blood vessel differ depending on eachtable. For example, in the case of the B−G difference (a value obtainedby subtracting the pixel value of the green signal from the pixel valueof the blue signal), the relationship between the B−G difference and theblood vessel depth shown in FIG. 17A is stored in a table that is usedin the first observation mode. Here, Ls indicates a B−G differenceindicating the boundary between the mucous membrane and the superficialblood vessel, and Ld indicates a B−G difference indicating the boundarybetween the mucous membrane and the medium-deep blood vessel.

On the other hand, the relationship between the B−G difference and theblood vessel depth shown in FIG. 17B is stored in a table that is usedin the second observation mode. In this table, a B−G difference Ls′ atthe boundary between the mucous membrane and the superficial bloodvessel is set to be larger than Ls, and a B−G difference Ld′ at theboundary between the mucous membrane and the medium-deep blood vessel isset to be larger than Ld. In addition, the relationship between the B−Gdifference and the blood vessel depth shown in FIG. 17C is stored in atable that is used in the second observation mode. In this table, a B−Gdifference Ls″ at the boundary between the mucous membrane and thesuperficial blood vessel is set to be smaller than Ls, and a B−Gdifference Ld″ at the boundary between the mucous membrane and themedium-deep blood vessel is set to be smaller than Ld.

The G/B ratio is a value obtained by dividing the green signal by theblue signal, the G−B difference is a value obtained by subtracting theblue signal from the green signal, the B/(B+G) ratio is a value obtainedby dividing the blue signal by the sum of the blue signal and the greensignal, the G/(B+G) ratio is a value obtained by dividing the greensignal by the sum of the blue signal and the green signal, the B/R ratiois a value obtained by dividing the blue signal by the red signal, theR/B ratio is a value obtained by dividing the red signal by the bluesignal, the B−R difference is a value obtained by subtracting the redsignal from the blue signal, the R−B difference is a value obtained bysubtracting the blue signal from the red signal, and the B/Y ratio is avalue obtained by dividing the green signal by the yellow signal (yellowsignal is a signal having wavelength information of 500 nm to 700 nm).

What is claimed is:
 1. An endoscope system, comprising: an electronicendoscope that comprises an illumination device for irradiating asubject with illumination light including a blue component and a greencomponent and an image signal acquisition device for acquiring two ormore color signals having different pieces of color information byreceiving and imaging return light from the subject using an imagingelement; a processor device that generates a multi-color image formedfrom calculated values obtained by performing predetermined calculationfor each pixel using the two or more color signals; and generates atleast one of a first layer blood vessel extraction image, which isobtained by extracting a first layer blood vessel at a specific depthfrom the multi-color image, or a second layer blood vessel extractionimage, which is obtained by extracting a second layer blood vessel at aposition deeper than the first layer blood vessel from the multi-colorimage, by performing blood vessel extraction processing, which differsdepending on each of a plurality of observation modes, on themulti-color image; and a plurality of calculated value tables, whichstore a correlation between a mucous membrane, the first layer bloodvessel, and the second layer blood vessel of the subject and thecalculated values, wherein the processor further generates at least oneof the first layer blood vessel extraction image or the second layerblood vessel extraction image by performing blood vessel extractionprocessing using a calculated value table corresponding to the setobservation mode, the calculated value table is set for each of theplurality of observation modes, wherein in each of the calculated valuetables, a calculated value indicating a boundary between the mucousmembrane and the first layer blood vessel is stored as a first boundaryvalue, and a calculated value indicating a boundary between the mucousmembrane and the second layer blood vessel is stored as a secondboundary value, and the first and second boundary values differdepending on each calculated value table.
 2. The endoscope systemaccording to claim 1, wherein the plurality of observation modes aremodes for improving visibility of a blood vessel in a predetermined partof the subject, and each of the observation modes is set for eachpredetermined part.
 3. The endoscope system according to claim 2,further comprising: a blood vessel enhancement image or suppressionimage generation device for generating a first layer blood vesselenhancement image or suppression image, in which the first layer bloodvessel is enhanced or suppressed, using the first layer blood vesselextraction image, or generating a second layer blood vessel enhancementimage or suppression image, in which the second layer blood vessel isenhanced or suppressed, using the second layer blood vessel extractionimage.
 4. The endoscope system according to claim 3, further comprising:a display device for displaying at least one of the first layer bloodvessel enhancement image or suppression image or the second layer bloodvessel enhancement image or suppression image.
 5. The endoscope systemaccording to claim 2, wherein the illumination device simultaneouslyirradiates blue narrowband light and fluorescent light that iswavelength-converted by a wavelength conversion member using the bluenarrowband light, as the illumination light, toward the subject, and theimage signal acquisition device images the subject, to which the bluenarrowband light and the fluorescent light are irradiatedsimultaneously, using a color imaging element.
 6. The endoscope systemaccording to claim 2, wherein the illumination device sequentiallyirradiates blue narrowband light and green narrowband light, as theillumination light, toward the subject, and the image signal acquisitiondevice images the subject sequentially using a monochrome imagingelement whenever the blue narrowband light and the green narrowbandlight are sequentially irradiated.
 7. The endoscope system according toclaim 2, wherein the color signals include a blue signal havinginformation of a blue component and a green signal having information ofa green component, and the multi-color image is a B/G image having a B/Gratio obtained by dividing the blue signal by the green signal for eachpixel.
 8. The endoscope system according to claim 1, further comprising:a blood vessel enhancement image or suppression image generation devicefor generating a first layer blood vessel enhancement image orsuppression image, in which the first layer blood vessel is enhanced orsuppressed, using the first layer blood vessel extraction image, orgenerating a second layer blood vessel enhancement image or suppressionimage, in which the second layer blood vessel is enhanced or suppressed,using the second layer blood vessel extraction image.
 9. The endoscopesystem according to claim 8, further comprising: a display device fordisplaying at least one of the first layer blood vessel enhancementimage or suppression image or the second layer blood vessel enhancementimage or suppression image.
 10. The endoscope system according to claim9, wherein the illumination device simultaneously irradiates bluenarrowband light and fluorescent light that is wavelength-converted by awavelength conversion member using the blue narrowband light, as theillumination light, toward the subject, and the image signal acquisitiondevice images the subject, to which the blue narrowband light and thefluorescent light are irradiated simultaneously, using a color imagingelement.
 11. The endoscope system according to claim 9, wherein theillumination device sequentially irradiates blue narrowband light andgreen narrowband light, as the illumination light, toward the subject,and the image signal acquisition device images the subject sequentiallyusing a monochrome imaging element whenever the blue narrowband lightand the green narrowband light are sequentially irradiated.
 12. Theendoscope system according to claim 8, wherein the illumination devicesimultaneously irradiates blue narrowband light and fluorescent lightthat is wavelength-converted by a wavelength conversion member using theblue narrowband light, as the illumination light, toward the subject,and the image signal acquisition device images the subject, to which theblue narrowband light and the fluorescent light are irradiatedsimultaneously, using a color imaging element.
 13. The endoscope systemaccording to claim 8, wherein the illumination device sequentiallyirradiates blue narrowband light and green narrowband light, as theillumination light, toward the subject, and the image signal acquisitiondevice images the subject sequentially using a monochrome imagingelement whenever the blue narrowband light and the green narrowbandlight are sequentially irradiated.
 14. The endoscope system according toclaim 8, wherein the color signals include a blue signal havinginformation of a blue component and a green signal having information ofa green component, and the multi-color image is a B/G image having a B/Gratio obtained by dividing the blue signal by the green signal for eachpixel.
 15. The endoscope system according to claim 1, wherein theillumination device simultaneously irradiates blue narrowband light andfluorescent light that is wavelength-converted by a wavelengthconversion member using the blue narrowband light, as the illuminationlight, toward the subject, and the image signal acquisition deviceimages the subject, to which the blue narrowband light and thefluorescent light are irradiated simultaneously, using a color imagingelement.
 16. The endoscope system according to claim 1, wherein theillumination device sequentially irradiates blue narrowband light andgreen narrowband light, as the illumination light, toward the subject,and the image signal acquisition device images the subject sequentiallyusing a monochrome imaging element whenever the blue narrowband lightand the green narrowband light are sequentially irradiated.
 17. Theendoscope system according to claim 1, wherein the color signals includea blue signal having information of a blue component and a green signalhaving information of a green component, and the multi-color image is aB/G image having a B/G ratio obtained by dividing the blue signal by thegreen signal for each pixel.
 18. The endoscope system according to claim1, wherein the color signals include a blue signal having information ofa blue component and a green signal having information of a greencomponent, and the multi-color image is a B/G image having a B/G ratioobtained by dividing the blue signal by the green signal for each pixel.19. A processor device for an endoscope system including an electronicendoscope that irradiates a subject with illumination light including ablue component and a green component and acquires two or more colorsignals having different pieces of color information by receiving andimaging return light from the subject using an imaging element,comprising: a multi-color image generation unit for generating amulti-color image formed from calculated values obtained by performingpredetermined calculation for each pixel using the two or more colorsignals; and a blood vessel extraction image generation unit forgenerating at least one of a first layer blood vessel extraction image,which is obtained by extracting a first layer blood vessel at a specificdepth from the multi-color image, or a second layer blood vesselextraction image, which is obtained by extracting a second layer bloodvessel at a position deeper than the first layer blood vessel from themulti-color image, by performing blood vessel extraction processing,which differs depending on each of a plurality of observation modes, onthe multi-color image, wherein the blood vessel extraction imagegeneration unit includes a plurality of calculated value tables, whichstore a correlation between a mucous membrane, the first layer bloodvessel, and the second layer blood vessel of the subject and thecalculated values, and a blood vessel extraction image generationsection that generates at least one of the first layer blood vesselextraction image or the second layer blood vessel extraction image byperforming blood vessel extraction processing using a calculated valuetable corresponding to the set observation mode, the calculated valuetable is set for each of the plurality of observation modes, wherein ineach of the calculated value tables, a calculated value indicating aboundary between the mucous membrane and the first layer blood vessel isstored as a first boundary value, and a calculated value indicating aboundary between the mucous membrane and the second layer blood vesselis stored as a second boundary value, and the first and second boundaryvalues differ depending on each calculated value table.
 20. An imageprocessing method performed in an endoscope system including anelectronic endoscope that irradiates a subject with illumination lightincluding a blue component and a green component and acquires two ormore color signals having different pieces of color information byreceiving and imaging return light from the subject using an imagingelement, the image processing method comprising: generating amulti-color image formed from calculated values obtained by performingpredetermined calculation for each pixel using the two or more colorsignals; and generating at least one of a first layer blood vesselextraction image, which is obtained by extracting a first layer bloodvessel at a specific depth from the multi-color image, or a second layerblood vessel extraction image, which is obtained by extracting a secondlayer blood vessel at a position deeper than the first layer bloodvessel from the multi-color image, by performing blood vessel extractionprocessing, which differs depending on each of a plurality ofobservation modes, on the multi-color image, wherein the blood vesselextraction processing generates at least one of the first layer bloodvessel extraction image or the second layer blood vessel extractionimage by using a calculated value table corresponding to the setobservation mode, the calculated value table stores a correlationbetween a mucous membrane, the first layer blood vessel, and the secondlayer blood vessel of the subject and the calculated values, thecalculated value table is set for each of the plurality of observationmodes, in each of the calculated value tables, a calculated valueindicating a boundary between the mucous membrane and the first layerblood vessel is stored as a first boundary value, and a calculated valueindicating a boundary between the mucous membrane and the second layerblood vessel is stored as a second boundary value, and the first andsecond boundary values differ depending on each calculated value table.